The elevators marked with the same number are interlinked with passages.
(Furthermore the passage interlinking the elevators marked 2 can be accessed
from the passage interlinking the elevators marked 4, but not vice versa).

To pass the maze: 1) Take the passages leading to the skull lever (A) and
flip it. This will activate the elevator C. 2) Go to elevator C. 3) get the
key from the Serpent Master and take the elevator (D) back up to the skull
lock (B). 4) Unlock the skull lock."

About the maps: The letters indicate secret rooms. The sign "X?" marks a
lock, lever, or button opening the secret room with the middle of the X
marking the exact location.

As you can see, the secret area C on the "Crypt 2" map and the secret room D
on the "Serpent Temple" map do not appear on the map on Volberding's site.